Methods for producing polyarylene ether resins are described, for example, in Japanese patent publication No. 21458/71 (U.S. Pat. Nos. 4,108,837 and 4,175,175) and Polymer, Vol. 18, page 359 (1977). As is well known, these polymers have already been commercially available and gained acceptance in various industrial fields.
With an advance in electric and electronic technology, the requirement of various industries for the properties of plastic materials has become increasingly rigorous, and for example, improved heat resistance, mechanical strength and solvent resistance have been desired. The industries are therefore looking forward to the development of materials which meet such a requirement.
Polyimide having the following recurring units ##STR2## is known to have excellent heat resistance and durability, but it has poor moldability. Further, since it does not melt, it cannot be molded by a usual injection molding technique. Moreover, it is insoluble in a solvent. Hence, one is compelled to resort to a complex process in the formation of polyimide film which comprises, for example, dissolving a polyamide acid intermediate (a polyimide precursor) in a solvent, forming a film from the solution, and then heat-treating the film.
Attempts have been made to improve the melt moldability of polyimide, but it has not been entirely successful to impart melt moldability while retaining the high heat resistance of polyimide. G. L. Brode et al. reported a polyimide resin derived from a diamine containing an ether bond and a sulfone bond and an aromatic tetracarboxylic anhydride, but stated that molding means for thermosplastic resins cannot be used for this polyimide resin (J. Polym. Sci., Poly. Chem., Vol. 12, pages 575-587 (1974)). In an attempt to improve the moldability of polyimide, a polyimide resin from benzophenonetetracarboxylic acid, methylenedianiline and tolylenediamine has also been used in practical application as described in Plastic Age, 1983, May 98. Because of its poor flowability, however, it is difficult to mold by injection molding or extrusion as in ordinary thermoplastic resins.
As shown above, it is extremely difficult to obtain polymers containing an aromatic imide bond and having good moldability although it is not certain whether the difficulty is due to a cross-linking reaction during polymerization or during molding.
A. Takekoshi et al. disclose in Japanese patent application (OPI) No. 103997/74 (corresponding to U.S. patent application Ser. No. 319,371 filed Dec. 29, 1972) that a polyimide from a specified aromatic tetracarboxylic acid represented by the following formula: ##STR3## wherein R represents a residue of a dihydric phenol and an ordinary aromatic diamine can be melt-molded. But this is a very rare case wherein a polyimide could be put to practical use by introducing the residue of a dihydric phenol into the tetracarboxylic acid component and thereby rendering the polymer thermoplastic.